Manufacture of 3,3,4,4-tetrahydroperfluoroalkanoates

ABSTRACT

Esters and other carboxylic acid derivatives of 3,3,4,4-tetrahydroperfluoroalkylcarboxylic acids are made by the iron promoted reaction of an ester of bromodifluoroacetic acid or other carboxylic acid derivatives and a (perfluoroalkyl)ethylene. The resulting products may be converted to the corresponding alkali metal or ammonium carboxylate slits which are useful as surfactants in fluoroolefin polymerizations.

FIELD OF THE INVENTION

Esters and other carboxylic acid derivatives of3,3,4,4-tetrahydroperfluoroalkylcarboxylic acids are made by the ironpromoted reaction of an ester of bromodifluoroacetic acid or othercarboxylic acid derivatives and a (perfluoroalkyl)ethylene.

TECHNICAL BACKGROUND

The salts of 3,3,4,4-tetrahydroperfluoroalkylcarboxylic acids (THPA) areuseful as surfactants in the polymerization of fluorinated olefins, forexample tetrafluoroethylene, for example see U.S. Pat. No. 5,763,552.This patent describes a synthesis for these compounds by the coppercatalyzed reaction of an ester of iododifluoroacetic acid with a(perfluoroalkyl)ethylene to form an iodo substituted ester of THPA,followed by reaction with a tin hydride to form a THPA ester. This 2step synthesis, which apparently gives 50-60% overall yields of theester, involves the use of expensive tin hydrides, which also pose adisposal problem. The THPA ester is then hydrolyzed to the THPA, andconverted to a salt by reaction with base. The salt is useful as asurfactant in fluoroolefin polymerizations.

C-M Hu et al., J. Chem. Soc., Chem. Commun., 1993, p. 72-73 report thesynthesis of 3-bromodifluoromethyl substituted propanoic acids andesters by the iron and CrCl₃ promoted reaction of dibromodifluoromethanewith various substituted and unsubstituted acrylic acids and esters. Nomention is made of using (perfluoroalkyl)ethylenes as reactants.

SUMMARY OF THE INVENTION

This invention concerns a process for the production of3,3,4,4-tetrahydroperfluoroalkanoates, comprising, contacting at about25° C. to about 150° C. in a liquid medium, iron, a first compound ofthe formula R¹CH═CH₂, and a second compound of the formula Br(R²)CFYwherein:

R¹ is perfluoroalkyl containing 1 to 30 carbon atoms;

R² is fluorine or perfluoroalkyl;

Y is —CN, CO₂H, —CO₂R³, or —C(O)NR⁴ ₂;

R³ is hydrocarbyl or substituted hydrocarbyl; and

each R⁴ is independently hydrogen, hydrocarbyl or substitutedhydrocarbyl.

DETAILS OF THE INVENTION

By hydrocarbyl is meant a univalent radical containing only carbon andhydrogen. By substituted hydrocarbyl herein is meant a hydrocarbyl groupthat contains one or more (types of) substituents that does notinterfere with the operation of the polymerization catalyst system.Suitable substituents in some polymerizations may include some or all ofhalo, ester, keto (oxo), amino, imino, carboxyl, phosphite, phosphonite,phosphine, phosphinite, thioether, amide, nitrile, and ether. Preferredsubstituents are halo, ester, amino, imino, carboxyl, phosphite,phosphonite, phosphine, phosphinite, thioether, and amide.

Herein by a 3,3,4,4-tetrahydroperfluoroalkanoate is meant a compound ofthe formula R¹CH₂CH₂CR²FY, wherein R¹, R² and Y are as defined above. Inpreferred first compounds R¹ is n-perfluoroalkyl containing 1 to 10carbon atoms. In preferred second compounds:

R² is perfluoro-n-alkyl containing 1 to 10 carbon atoms or fluorine,especially R² is fluorine; and/or

Y is —CO₂H or —CO₂R³ wherein R³ is alkyl, and especially preferably R³is alkyl containing 1 to 6 carbon atoms.

By a liquid medium is meant a liquid in which the first compound and thesecond compound are soluble. By soluble in this context is meant that atleast 1 weight percent, preferably at least 5 weight percent, of each ofthe first and second compound will dissolve in the liquid at 30° C.Useful liquid media are organic liquids, particularly more polar organicliquids such as alcohols, ethers, ketones, etc. Preferred materials forthe liquid medium are aliphatic alcohols containing 1 to 8 carbon atoms,more preferably 1 to 4 carbon atoms, and especially preferably methanolor ethanol. When an alcohol is used as the liquid medium, if Y is —CO₂Hor —CO₂R³, and R³ is not the same as the alkyl group of the alcohol, theresulting R³ in the product may be the alkyl group of the alcohol. Inother words esterification or transesterification may take place. Forexample if Y is —CO₂R³, and R³ is ethyl, and the liquid medium ismethanol, R³ in the product may be (mostly) methyl.

The iron (metal) present in the reaction need not be in any particularform, but it is preferred that it have a relatively high surface area,for example be in the form of iron powder or so-called iron filings.However the source of the iron can even be the reactor vessel, forexample steel or another iron alloy.

If desired CrCl₃ may also be present in the reaction, although it ispreferred that it not be present.

The molar ratio of the ingredients is not critical, but typically amolar excess of the first compound over the second compound will bepresent, and a molar excess of iron over the first compound will also bepresent. This usually makes the most efficient use of the normally mostexpensive compound, the second compound. The concentrations of thereactants in the liquid medium are not critical, typical concentrationsbeing illustrated in the Examples.

The time of reaction is not critical, a period of time sufficient toachieve the desired conversion at the temperature used being useful.Typical reaction times are 1 to 100 hours, more typically 3 to 50 hours.The process is run at about 30° C. to about 150° C., preferably about50° C. to about 100° C. The pressure at which the process is run is alsonot critical, atmospheric pressure being convenient. In the case ofrunning the process at temperatures above the boiling point(s) of one ormore of the ingredients, it may be useful to run the process in apressure vessel at autogenous pressure.

No matter what Y is in the first compound, it may be converted to acarboxyl group (if it is not already a carboxyl group) by hydrolysisusing standard organic chemical techniques, see for instance U.S. Pat.No. 5,763,552, which is hereby included by reference. The carboxyl groupmay then be converted to a salt, preferably an ammonium or alkali metalsalt, which is then may be used as a surfactant in a fluoroolefin freeradical polymerization, again see U.S. Pat. No. 5,763,552.

In the Examples pressures are gauge pressures, except where noted. Inthe Examples the following abbreviations are used:

Et—ethyl

EtOH—ethanol

GC-MS—coupled gas chromatography-mass spectroscopy

Me—methyl

MeOH—methanol

i-PrOH—isopropanol

PrOH—n-propanol

PFBE—(perfluorobutyl)ethylene

Pr—propyl

i-Pr—isopropyl

PFBE was obtained from E. I. du Pont de Nemours and Company, Wilmington,Del., U.S.A., iron powder was obtained from Aldrich Chemical Co.,Milwaukee, Wis., U.S.A., and ethyl bromodifluoroacetate was obtainedfrom SynQuest Lab., Inc., Alachua, Fla., U.S.A.

EXAMPLE 1 Synthesis of C₄F₉CH₂CH₂CF₂CO₂Et in EtOH

A mixture of PFBE (36.9 g, 150 mmol), ethyl bromodifluoroacetate (20.3g, 100 mmol), Fe (10 g, 200 mmol), and EtOH (150 ml) was refluxed for 40h. The internal temperature rose from an initial temperature of 64° C.to 73° C. at the end of the reaction. The ¹⁹F NMR analysis of themixture indicated that it contained a trace amount of ethylbromodifluoroacetate, and C₄F₉CH₂CH₂CF₂CO₂Et and HCF₂CO₂Et were formedin 76:24 ratio. Excess PFBE and several minor products were alsoobserved. The liquid reaction mixture was transferred to another flaskand distilled under full vacuum The receiver was cooled by liquid N₂bath. The distillate was then fractional distilled to give 8 g of theester product. The residue in the second flask was mixed with 100 ml ofHCl (1N) and extracted with ether (200 ml). The ether solution waswashed with HCl (1N, 2×50 ml), dried over Na₂SO₄, and concentrated togive a liquid, which was distilled at reduced pressure to give 11 g ofthe ester. The distillation residue was treated with KOH (10%) andextracted with CH₂Cl₂. The aqueous solution was acidified by HCl (6N) topH=1, and extracted with ether. The ether extracts were washed withwater, dried over Na₂SO₄, and concentrated to give the acid (4 g), whichcontained a small amount of impurities. These impurities have not beenidentified. The yields were 51% for the ester and 12% for thecorresponding acid.

C₄F₉CH₂CH₂CF₂CO₂Et: ¹H NMR (CDCl₃) 1.31 (t, J=7 Hz, 3H), 2.40 (m, 4H),4.38 (q, J=7 Hz, 2H) ppm. ¹⁹F NMR (CDCl₃) −81.6 (t, J=9 Hz, 3F), −107.4(t, J=15 Hz, 2F), −115.2 (t, J=15 Hz, 2F), −124.8 (m, 2F), −126.5 (m,2F) ppm. ¹³C NMR (CDCl₃) 13.7, 23.9 (t, J=23 Hz), 26.1 (t, J=24 Hz),63.3, 114.8 (t, J=252 Hz), 163.3 (t, J=32 Hz), 108.3-120.8 (m) ppm. MS:371 (M⁺+1, 0.9%), 343 (1.4%), 323 (5.7%), 297 (22.3%), 277 (27.3%), 227(17.5%), 219 (1.8%), 169 (7.8%), 119 (16%), 69 (96%), 64 (100).

EXAMPLE 2 Synthesis of C₄F₉CH₂CH₂CF₂CO₂Me in MeOH

A 210 ml shaker tube was charged with PFBE (18.5 g, 75 mmol), ethylbromodifluoroacetate (10 g, 50 mmol), Fe (4 g, 80 mmol), and MeOH (50ml). The mixture was heated at 75° C. for 30 h. After removal of excessFe, the solution was distilled to remove MeOH. The residue was thendistilled at reduced pressure to give A (5 g), B (8 g), and C theresidue (B is pure product and A contained MeOH). The original MeOHdistillate contained a small amount of the product and was fractionatedto give a residue. The residue was combined with A and redistilled atreduced pressure to afford 4 g of the product (D). The residue C wasmixed with HCl (1N) and extracted with ether. The ether solution waswashed with HCl (1N, 2×50 ml), dried over Na₂SO₄, and concentrated togive a liquid, which was distilled at reduced pressure to give 1.0 g ofthe ester (E). The overall yield of ester was 13 g (B+D+E), 74%. All ofthe products were mainly methyl ester with a small amount of ethylester.

EXAMPLE 3 Synthesis of C₄F₉CH₂CH₂CF₂CO₂Pr-i in i-PrOH

A mixture of PFBE (1.88 g), ethyl bromodifluoroacetate (1.03 g), Fe(0.46 g), and i-PrOH (5 ml) was refluxed for 15 h. ¹⁹F NMR analysis ofthe mixture indicated a 68% conversion of the ethyl bromodifluoroacetateand 73% selectivity to the desired ester. GC-MS analysis of the mixturerevealed that the product was i-Pr ester.

EXAMPLE 4 Synthesis of C₄F₉CH₂CH₂CF₂CO₂Pr in PrOH

A mixture of PFBE (1.80 g), ethyl bromodifluoroacetate (0.99 g), Fe(0.43 g), and i-PrOH (5 ml) was refluxed for 15 hours. ¹⁹F NMR analysisof the mixture indicated an 88% conversion of ethylbromodifluoroacetate, and 76% selectivity to the desired ester. GC-MSanalysis of the mixture revealed that the product was the correspondingn-propyl ester.

EXAMPLE 5 Synthesis of C₆F₁₃CH₂CH₂CF₂CO₂Me in MeOH

A 210 ml shaker tube was charged with (perfluorohexyl)ethylene (12.5 g),ethyl bromodifluoroacetate (5.0 g), Fe (2 g), and MeOH (25 ml). Themixture was heated at 75° C. for 30 h. After removal of excess Fe, thesolution was distilled to remove MeOH. The residue was then distilled atreduced pressure to give the product, 6.9 g, bp 63-64° C. at 70 Pa(absolute), yield 61%. ¹H NMR (CDCl₃) 2.41 (m, 4H), 3.95 (s, 3H) ppm.¹⁹F NMR (CDCl₃) −81.4 (t, J=11 Hz, 3F), −107.3 (t, J=15 Hz, 2F), −115.0(t, J=15 Hz, 2F), −122.3 (2F), −123.3 (2F), −123.8 (m, 2F), −126.6 (m,2F) ppm. ¹³C NMR (CDCl₃) 23.9 (tt, J=23, 5 Hz), 26.2 (tt, J=25, 4 Hz),53.5, 114.8 (t, J=251 Hz), 163.8 (t, J=33 Hz), 108.3-119.7 (m) ppm.

EXAMPLE 6 Synthesis of C₈F₁₇CH₂CH₂CF₂CO₂Me in MeOH

A 210 ml shaker tube was charged with (perfluorooctyl)ethylene (16.0 g),ethyl bromodifluoroacetate (5.0 g), Fe (2 g), and MeOH (25 ml). Themixture was heated at 75° C. for 30 h. After removal of excess Fe, thesolution was concentrated to give a residue which was extracted bymethylene chloride. The methylene chloride extract was concentrated anddistilled at reduced pressure to give the product A, 7.0 g, bp, 71-2° C.at 40 Pa (absolute). The distillation residue was dissolved in ether andwashed with HCl (1N) and water, concentrated, and distilled at reducedpressure to afford another portion of the product B, 1.5 g. Total yield7.0+1.5=8.5 g, 62%. ¹H NMR (CDCl₃) 2.41 (m, 4H), 3.92 (s, 3H) ppm. ¹⁹FNMR (CDCl₃) −81.4 (t, J=9 Hz, 3F), −107.3 (t, J=15 Hz, 2F), −115.0 (t,J=15 Hz, 2F), −122.2 (2F), −122.4 (4F), −123.2 (2F), −123.8 (m, 2F),−126.6 (m, 2F) ppm. ¹³C NMR (CDCl₃) 23.9 (t, J=22 Hz), 26.2 (t, J=24Hz), 53.6, 163.8 (t, J=32 Hz), 108.1-119.7 (m) ppm.

EXAMPLE 7 Reaction of C₄F₉CH═CH₂, BrCF₂CO₂Et, and Fe in Ethyl Ether

A mixture of perfluorohexylethylene (2.0 g, 8.1 mmol), ethylbromodifluoroacetate (1.0 g, 4.9 mmol), Fe (0.5 g, 9 mmol), and ethylether (10 ml) was heated to 75° C. in an autoclave for 30 h. ¹⁹F NMRanalysis of the reaction mixture indicated 10% conversion and 95%selectivity to C₄F₉CH₂CH₂CF₂CO₂Et.

EXAMPLE 8 Reaction of C₄F₉CH═CH₂, BrCF₂CO₂Et, and Fe in Acetone

A mixture of perfluorohexylethylene (2.0 g, 8.1 mmol), ethylbromodifluoroacetate (1.0 g, 4.9 mmol), Fe (0.5 g, 9 mmol), and acetone(10 ml) was heated to 75° C. in an autoclave for 30 h. ¹⁹F NMR analysisof the reaction mixture indicated that it contained BrCF₂CO₂Et (2%),HCF₂CO₂Et (41%), C₃F₇CF═CHCH₂CF₂CO₂Et (51%), and C₄F₉CH₂CH₂CF₂CO₂Et(6%).

EXAMPLE 9 Reaction of C₆F₁₃CH═CH₂, BrCF₂CO₂Et, Fe and CrCl₃ in EtOH

A mixture of perfluorohexylethylene (1.95 g, 5.6 mmol), ethylbromodifluoroacetate (0.94 g, 4.6 mmol), Fe (0.5 g, 9 mmol), CrCl₃ (0.15g), and EtOH (10 ml) was gently refluxed for 15 h. The solids wereremoved by filtration and the filtrate was analyzed by ¹⁹F NMR andGC-MS, which indicated that the mixture contained BrCF₂CO₂Et,C₆F₁₃CH₂CH₂CF₂CO₂Et, and HCF₂CO₂Et in a 17:49:34 ratio, as well asexcess perfluorohexylethylene.

The results of Examples 1-8 are summarized in Table 1.

TABLE 1 Preparation of 3,3,4,4-Tetrahydroperfluoroalkanoates Ex.Reactants and Conditions Results 1 C₄F₉CH═CH₂/BrCF₂CO₂Et/C₄F₉CH₂CH₂CF₂CO₂Et 51%^(a) Fe/EtOH C₄F₉CH₂CH₂CF₂CO₂H 12% reflux 40 h 2C₄F₉CH═CH₂/BrCF₂CO₂Et/ C₄F₉CH₂CH₂CF₂CO₂Me 74%^(a) Fe/MeOH 75° C. 30 h 3C₄F₉CH═CH₂/BrCF₂CO₂Et/ 68% conversion^(b) 73% Fe/i-PrOH selectivity toreflux 15 h C₄F₉CH₂CH₂CF₂CO₂i-Pr 4 C₄F₉CH═CH₂/BrCF₂CO₂Et/ 88%conversion^(b) 76% Fe/PrOH selectivity to reflux 15 h C₄F₉CH₂CH₂CF₂CO₂Pr5 C₆F₁₃CH═CH₂/BrCF₂CO₂Et/ C₆F₁₃CH₂CH₂CF₂CO₂Me 61%^(a) Fe/MeOH 75° C. 30h 6 C₈F₁₇CH═CH₂/BrCF₂CO₂Et/ C₈F₁₇CH₂CH₂CF₂CO₂Me 62%^(a) Fe/MeOH 75° C.30 h 7 C₄F₉CH═CH₂/BrCF₂CO₂Et/ 10% conversion^(b) 95% Fe/Et₂O selectivityto 75° C. 30 h C₄F₉CH₂CH₂CF₂CO₂Et 8 C₄F₉CH═CH₂/BrCF₂CO₂Et/ HCF₂CO₂Et41%^(b) Fe/Acetone C₃F₇CF═CHCH₂CF₂CO₂Et 51% 75° C. 30 hC₄F₉CH₂CH₂CF₂CO₂Et  6% ^(a)Isolated yields. ^(b)The data was based on¹⁹F NMR analysis of the reaction mixture.

What is claimed is:
 1. A process for the production of a3,3,4,4-tetrahydroperfluoroalkanoate, consisting of contacting at about25° C. to about 150° C. in a liquid medium, iron, a first compound ofthe formula R¹CH═CH₂, and a second compound of the formula Br(R²)CFYwherein: R¹ is perfluoroalkyl containing 1 to 30 carbon atoms; R² isfluorine or perfluoroalkyl; Y is —CN, CO₂H, —CO₂R³, or —C(O)NR⁴ ₂; R³ ishydrocarbyl or substituted hydrocarbyl; and each R⁴ is independentlyhydrogen, hydrocarbyl or substituted hydrocarbyl.
 2. The process asrecited in claim 1 wherein said liquid medium is an alkyl alcohol having1 to 4 carbon atoms.
 3. The process as recited in claim 1 wherein saidliquid medium is methanol or ethanol.
 4. The process as recited in claim1 wherein R¹ is perfluoro-n-alkyl containing 1 to 10 carbon atoms. 5.The process as recited in claim 1 wherein R² is fluorine.
 6. The processas recited in claim 1 wherein Y is —CO₂H or —CO₂R³ wherein R³ is alkyl.7. The process as recited in claim 1 wherein said temperature is about50° C. to about 100° C.
 8. The process as recited in claim 1 whereinsaid liquid medium is an alkyl alcohol having 1 to 4 carbon atoms, R¹ isperfluoro-n-alkyl containing 1 to 10 carbon atoms, R² is fluorine, and Yis —CO₂H or —CO₂R³ wherein R³ is alkyl.
 9. The process as recited inclaim 8 wherein said liquid medium is methanol or ethanol.
 10. Theprocess as recited in claim 8 wherein said temperature is about 50° C.to about 100° C.
 11. The process as recited in claim 1 wherein CrCl₃ isalso present.
 12. The process as recited in claim 1 comprising theadditional steps of forming a compound in which Y is —CO₂H, and formingan alkali metal or ammonium salt of said —CO₂H group.
 13. The process asrecited in claim 12 comprising the additional step of polymerizing afluoroolefin in a free radical polymerization in the presence of saidsalt.